Zama C1Q Check Valve Replacement with Pics

ricky86

LawnSite Silver Member
The check valves, IN the carb, are suppose to close when the bulb is used. If they were not working (stuck open), the primer wouldn't work very well, if at all. They prevent air from being sucked into the metering chamber, through the main and idle circuit, during the priming process. If air is sucked in, the purge process can't work. If they are stuck closed, no fuel can enter the engine, so it can't flood. You carb might have a slightly rich setting on the inlet needle, among other things. But if it starts, do you care?
There seems to be some dispute if they serve any purpose during running, which is OK. It's sort of a theory vs actual.
 

BigFish

LawnSite Fanatic
Location
chesapeake, va
The check valves, IN the carb, are suppose to close when the bulb is used. If they were not working (stuck open), the primer wouldn't work very well, if at all. They prevent air from being sucked into the metering chamber, through the main and idle circuit, during the priming process. If air is sucked in, the purge process can't work. If they are stuck closed, no fuel can enter the engine, so it can't flood. You carb might have a slightly rich setting on the inlet needle, among other things. But if it starts, do you care?
There seems to be some dispute if they serve any purpose during running, which is OK. It's sort of a theory vs actual.

No disputing the facts. Go here http://www.zamacarb.com/pdfs/TechGuide_2007.pdf and READ paragraph 5 under IDLE OPERATION. Should make it clearer for ya.

Oli, it sounds like the check valve in the primer bulb base is bad/weak, which is pressurizing the metering chamber and squirting gas out the main nozzle.
 

BigFish

LawnSite Fanatic
Location
chesapeake, va
My apologies to Maico490 for unintended hijacking.
As mentioned before, your photos and narrative are great!!!

Just havin' a little fun.
 

jkilov

LawnSite Bronze Member
Location
MS
Well no. You stated that the main check valve prevents air from entering the carb at idle. That is not true.
Well it is, and all butterfly membrane carbs, regardles if they have bulbs or not, need one.

Your question about 4-stroke float carbs needing check valves is kind of puzzling. Float and membrane carbs are not alike, not even close. Membrane carbs have "wet" idle & main circuits supplying fuel to multiple nozzles and any air will badly screw up metering. Float carbs have only one nozzle, the screw type part that holds the bowl, which mixes fuel with bleed air to form emulsion. This then travels up the emulsion tube or tubes to the throat or idle circuit. Some people mistake the emulsion tube for the main nozzle, which is debatable. So I dont quite get the question? There already is air the emulsion tube, it's coming from the bleed vent to make the carb work properly. If you meant what if it entered the nozzle at the bottom, well it can't cause fuel is always being drawn out, there's no idle detour like on membrane carbs.
 
OP
M

Maico490

LawnSite Member
Location
SW England
I haven't looked back at this thread for a while but looks like there have been a few toys thrown out of the pram.
I can confirm that the check valves are 100% needed for correct running. At full throttle there is enough depression across the carb to overcome the main check valve and fuel flows through it. This is the case even if the check valve isn't working. However at idle if it is defective instead of fuel being drawn from the metering chamber air will be drawn back through the main jet and the engine will die.
 

ed2hess

LawnSite Fanatic
Any you wouldn't need a membrane carb to begin with, just a regular float. 2-strokes and membrane carbs go hand in hand, both operate in any position. Oh and Dave, I ride bikes too :drinkup:


Zamba sounds like house dance or voodoo. Anyway, Zama (owned by Stihl) had several faulty batches of carbs. Something with aluminum materials developing hairline cracks making the carbs leak internally, these can't be fixed. The correct way to diagnose it is to do a carb leak down test. Since 3 new carbs cost some money I would try to !properly! clean them.

Did they identify the lot numbers that were faulty? My unit is a RB7577A
 

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